Self-sealing threaded fastener and process for making the same

ABSTRACT

A method of making a reusable, self-sealing threaded fastener having an integral seal and which does not require additional curing or heating after installation is disclosed. The sealant is a soft pliable olefin based material designed to flow between the bearing shoulder and threads of the fastener, and the abutting bearing surface of a receptacle as the fastener is tighted into the receptacle thereby creating a tight seal.

This is a divisional of copending application Ser. No. 07/621512 filedon Nov. 30, 1990, now U.S. Pat. No. 5,141,375, patented Aug. 25, 1992.

BACKGROUND OF THE INVENTION

This invention relates to fasteners and is more specifically related toa self-sealing threaded fastener for sealing in cooperation with acomplementary receptacle.

It is well known that helical threaded fasteners do not form water-tightengagement with a complementary surface or mating fastener unless agasket or seal of some sort is supplied between the threaded portion ofthe fastener and the receptacle or fastener to seal the valleys createdby the roots and crests of the threads. Such a gasket is shown in U.S.Pat. No. 2,775,917 issued to W. C. Ferguson on Jan. 1, 1957, whichdescribes a sheet metal nut with an integral gasket that is adapted toflow into and fill the valleys created by the sheet metal thread.

It is also known to provide self-locking fasteners. By nature, suchfasteners are not self-sealing. An example of a self-locking fastener isshown in U.S. Pat. No. 3,746,068 issued to Deckert et al on Jul. 17,1973, which shows an encapsulated adhesive applied directly to thethreads of a threaded fastener, wherein said adhesive is pressureactuated as the threaded fastener is turned into a tapped receptacle,for permanently bonding the threaded fastener in the receptacle. Manyother similar type devices are known for providing self-locking threadedfasteners such as, by way of example, those shown in U.S. Pat. No.3,061,455 issued to Anthony on Oct. 30, 1962 and U.S. Pat. No. 3,022,917issued to Jedlicka on Feb. 20, 1962.

A self-sealing mechanical fastener with a self-contained gasket is shownin U.S. Pat. No. 3,472,301 issued to Pearce on Oct. 14, 1969. As thereshown, a flowable sealant is introduced into a cavity provided in thecenter of the threaded shank of the screw fastener. A plurality ofcapillaries or channels communicate the sealant cavity with theperipheral threaded area of the shank. The screw fastener is used intypical fashion, and after being secured in a suitable receptacle, adowel is placed into the sealant filled cavity for forcing the flowablesealant out through the capillaries into the valleys between the rootsand crests of the threaded connection to provide for a seal.

The sealing mechanism used with threaded fasteners of the prior art allhave the same disadvantage in that each requires a plurality of steps toboth secure the fastener in the receptacle and to activate the sealingmechanism. For example, in U.S. Pat. No. 2,775,917 discussed above, thesealing nut must be applied directly to the male threaded fastenereither before or after the male threaded fastener is used to secure aplurality of elements to one another. In U.S. Pat. No. 3,472,301, adowel or similar tool must be used to activate the sealant after thethreaded fastener is in place. In addition, the prior art sealingmechanisms are quite costly, and not as reusable as desired.Furthermore, the sealing mechanisms of the prior art do not provideadequate filling and sealing between the two mating fasteners in certaininstallations.

While the self-locking fasteners are designed to be self-energizingduring the normal thread tightening function, the self-locking designsof the prior art are not intended to and do not provide a gasket-typesealing function.

SUMMARY OF THE INVENTION

The subject invention provides a threaded fastener with an integralsealing element, wherein the engaging surface of a threaded fastenerincludes a soft, pliable, flowable adhesive adhered thereto. As thethreaded fastener is installed into a complementary receptacle, and theengaging surface is brought into abutting relationship with acomplementary bearing surface on the receptacle, the sealant flowsaround the engaging surface and into the valleys created by the rootsand crests of the threaded portion to provide a tight gasket-type sealbetween the fastener and the receptacle.

In its preferred form, the sealant is a soft, pliable thermoplastic suchas, by way of example, an olefin, polyolefin or the like. The sealantmay be applied by spray coating fine powdered particles of the materialdirectly onto the engaging surface and thread area of a heated threadedfastener in sufficient quantities to build-up an appropriate gasket toprovide proper sealing. In addition, the gasket, formed when cooled,promotes free flow of the sealant as the threaded fastener is installedand tightened into position in a suitable receptacle.

In the preferred form, the olefin coating may be sprayed directly onto aheated threaded fastener which when cooled, forms a sealing gasket. Avacuum source may be used to create a low pressure zone near thefastener during the spraying process to remove any excess sealantparticles from the atmosphere preventing stray deposits on the fastener.

The threaded fastener with an integral sealant of the present inventionhas proven to provide a good moisture-tight gasket or seal between thefastener and a complementary receptacle. The sealant flows adequatelyinto the openings between the engaging surface of the threaded fastenerand the complementary bearing surface on the receptacle, as well as intothe valleys created by the roots and crests of the threaded members.

It is, therefore, an object and feature of the subject invention toprovide for a self-sealing threaded fastener. It is a further object andfeature of the invention to provide for an integral gasket-type sealwhich is self-energized upon screw tightening the threaded fastener intoa suitable receptacle

It is an additional object and feature of the invention to provide for amethod of making a threaded fastener with an integral sealing element.It is also an object of the present invention to provide a costeffective fastener having an integral sealing element which is reusableand has improved filling and sealing qualities.

Other objects and features of the invention will be readily apparentfrom the accompanying drawing and description.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a plan view of a threaded fastener with an integral sealingelement made in accordance with the present invention.

FIG. 2 is a side view, partially in section, of the threaded fastener ofFIG. 1 shown as used, installed into an engaging receptacle.

FIG. 3 is a diagrammatic illustration of a process for making a threadedfastener with an integral sealing element in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A threaded fastener in accordance with the present invention isillustrated in FIG. 1. As there shown, the fastener 10 is a malethreaded fastener and includes an enlarged head 12 having asubstantially flat radial bearing or engaging surface 13 and a shank 14intersecting the engaging surface 13 and projecting outwardly therefrom.The shank 14 includes a helical thread 16 extending its entire length inthe well known manner. As may be appreciated, the fastener 10 may be anytype of threaded fastener including male and female threaded fastenershaving a threaded portion and an adjacent engaging surface. Asillustrated, fastener 10 is a male threaded fastener which may bestraight tapered, as shown, or angle tapered depending on application,in the manner well known to those skilled in the art.

In the preferred embodiment of the subject invention, a sealing material20 is applied to the area adjacent the engaging surface 13 and the upperend of the threaded shank 14. The sealing material 20 is a soft, pliablesealant such as a thermoplastic resin of the olefin or polyolefin type.A finely powdered olefin or polyolefin based material with a specificgravity of between 0.95 and 1.2 and a melting point of about 90° C. toabout 120° C. (about 194° F. to about 248° F.) known as Corvell® clear,part number 94-9002, manufactured by Morton International SpecialtyChemicals Group of Reading, Pa., has been shown to be a suitablepowdered material for defining a sealant material and providing therequired sealing performance in accordance with the present invention.

As shown in FIG. 2, when a plurality of elements 22 and 24 are to besecured to one another by means of the threaded fastener 10, a suitablereceptacle comprising the apertures 26a and 26b is provided in theelements 22 and 24 for receiving the shank 14 of the fastener 10. As theshank 14 is screw-tightened into the receptacles 26a and 26b, theengaging surface 13 is pulled into abutting relationship with thecomplementary bearing surface 23 of element 22. As the fastener 10 isturned into the receptacles 26a and 26b, the pliable, flowable sealantmaterial 20 fills the valleys 27 defined by the roots and crests of thethreads 16 and flows outwardly from the shank to fill the space betweenthe surfaces 13 and 23 to provide a tight sealing element or gasket.

In practice, using the polyolefin powder coating described above for thesealing material 20, the present invention has been successfullyemployed as wheel hub lock fasteners for off-road four-wheel drivevehicles and meets the sealing requirement of test specifications set bythe Ford Motor Company of Dearborn, Mich. for such wheel hubs.Specifically, fasteners of the present invention have been used on wheelhubs and provide a water-tight seal between the fastener and the securedelement when the wheel hub is fully submerged in twenty-four (24) inchesof standing water for a period of not less than two (2) minutes.

Furthermore, the self-sealing fastener of the present invention has beensuccessfully employed to seal a case assembly housing electroniccircuitry when the case was required to be secured to another member.Specifically, twelve (12) screws, similar to the threaded fastener 10illustrated in FIG. 1, were threaded into and out of an engagingreceptacle ten (10) times. It was found that the polyolefin material hadremained unchanged and intact on all (12) screws and did not adverselyaffect the ability to thread the screw into proper engagement. Moreover,these twelve (12) screws were then used in assembly of a commercial caseunit. The unit was fully submerged in water for 24 hours without anyincidents of leakage from any of the self-sealing screws. Accordingly,reused sealing fasteners of the present invention still provide adequatesealing performance. Further, in these tests, it was found and concludedthat the sealing fasteners of the present invention were superior to theprior art o-ring type seals in sealing performance, reusability andfastening retention.

Additional tests were conducted in which the fasteners of the presentinvention were placed in an environmental chamber where the temperatureand humidity levels were varied as follows:

Eight (8) thirty minute cycles at 70° C. with 98% humidity alternatedwith eight (8) thirty minute cycles at -10° C. and thereafter, a onehour period to reach ambient temperature.

The fasteners of the present invention were subjected to two (2) ofthese nine hour cycles while installed in a commercial case assembly forelectronic components as described above. This case assembly, afterundergoing two (2) nine hour environmental chamber cycles, was submergedin standing water for twenty-four (24) hours. None of the installedfasteners of the present invention leaked whatsoever and all of thesefasteners performed satisfactorily thereafter in a commercialinstallation.

The self-sealing fasteners of the subject invention may be used inconjunction with self-tapping screw forms as shown in FIG. 1, such as,by way of example, sheet metal screws and the like, or in conjunctionwith precision-threaded screws and nuts and tapped receptacles where amoisture-tight seal is required between the fastener and the securedelement.

A process for making a self-sealing threaded fastener 10 in accordancewith the present invention is diagrammatically illustrated in FIG. 3. Asthere shown, the threaded fastener 10 is secured in a fixture 28 withthe engaging surface 13 and the upper portion of the shank 14 exposed.The fasteners, including at least the head 12, the engaging surface 13and the upper portion of shank 14, is then heated to a temperature abovethe melting point of the powdered coating material. The fastener istypically heated to between about 300° F. and about 550° F. and morepreferably to between about 450° F. and about 525° F. Powdered coatingmaterial 20 is sprayed through nozzle 30, directly onto the heated shank14 and engaging surface 13 of the fastener 10 as shown at arrows 21. Apressurized supply of the powdered coating material is supplied bypressure and supply source 32 in the well known manner. In practice, thenozzle has an orifice with the dimensions of approximately 1" long byapproximately 1/8" high and the powdered coating particles are betweenabout 17 micrometers and about 180 micrometers in diameter. The meandiameter particle size being about 104 micrometers. The powder issprayed onto the engaging surface and shank of the threaded fastener ata pressure of approximately 34-45 standard cubic feet per hour (SCFH).

In the preferred embodiment of the invention, a vacuum source isprovided at 36 with an exhaust opening as shown at 34 to remove excesspowder particles from the atmosphere during the spraying process. Thevacuum draws negative pressure sufficient to draw any excess powderparticles away from the fastener thereby avoiding any unwanted powderapplication on the fastener. In the preferred embodiment the exhaustopening 34 is oval in shape and approximately 2" by 1" in size. However,any suitable vacuum exhaust opening can be used. In addition, it may bedesirable to provide a secondary air source utilized as an air curtain(not shown) to prevent powder material from being applied in undesirablelocations on the fastener.

The fixture 28 is designed to rotate 360° during the spraying process toprovide uniform distribution of the powdered coating on the engagingsurface and shank portion of the fastener 10. After the powdered coatingis sprayed onto the heated fastener 10, a cooling liquid (not shown) issprayed onto the fastener 10 to set the melted powdered coating materialwhich has been melted onto and bonded to the fastener. This coolingliquid may be water, water with a rust inhibitor, additive or the like.Subsequently, the fastener 10 is removed from fixture 28. Removal may beaccomplished by manually unthreading the fastener 10 from fixture 28 or,more preferably, fastener 10 is threaded onto fixture 28 by one threadthus allowing an air source to provide the force necessary to blowfastener 10 out of fixture 28. Finally, the coated sealing fasteners 10are deposited into a cooling and rust inhibiting liquid prior to use orpackaging for shipment.

While certain features and embodiments of the invention have beendisclosed herein, it will be readily understood that the inventionincludes all modifications and enhancements within the scope and spiritof the following claims.

I claim:
 1. A method of making a reusable, self-sealing threadedfastener having an integral seal, comprising the steps of:a. holding thefastener with an engaging surface and a threaded portion exposed forcoating; b. heating at least the engaging surface and the threadedportion of the fastener; c. applying a sealant material to the threadedportion and the engaging surface and the intersection thereof such thatsaid sealant material melts and bonds to the threaded portion and theengaging surface of the fastener; and d. curing the sealant materialprior to installation of said fastener into a receiving member; saidinstallation causing said sealant to form a watertight and airtightgasket about said fastener.
 2. The method of claim 1, wherein saidapplying step comprises spraying said sealant material onto the heatedfastener, and further including the step of providing a low pressurezone for drawing off excess sealant.
 3. The method of claim 1, whereinthe step of heating includes heating at least the engaging surface andthe threaded portion of the fastener to a temperature between about 450°F. and about 525° F.
 4. The method of claim 1, wherein said sealantmaterial is an olefin based material.
 5. The method of claim 1, whereinsaid sealant material is a polyolefin based material.
 6. The method ofclaim 1, wherein said sealant material is a thermoplastic having aspecific gravity between about 0.95 and about 1.2.
 7. The method ofclaim 1, wherein said sealant material is at least one of a finelypowdered olefin and polyolefin coating material.
 8. A method of making areusable, self-sealing threaded fastener with a threaded shank and ahead having an integral seal comprising the steps of:a. holding thefastener with the underside of said head defining a bearing surface andthreaded shank exposed; b. heating at least the exposed bearing surfaceand threaded shank of said fastener to a temperature above the meltingpoint of a sealant material to be applied to the fastener; c. spraying apowdered sealant material directly to the fastener in the exposed areaadjacent the intersection of the shank and bearing surface whereby saidsealant material melts on the exposed area adjacent the intersection ofthe shank and bearing surface of the fastener to form an integralsealing element on said fastener; d. drawing off excess powdered sealantmaterial not applied to the fastener; and e. curing the sealant materialprior to installation of said fastener into a receiving member; saidinstallation causes said sealant to form a watertight and airtightgasket about said fastener.
 9. The method of claim 8, wherein the stepof heating includes heating at least the exposed bearing surface and thethreaded shank to a temperature between about 450° F. and about 525° F.